The present invention relates to a last on which a shoe shaft can be mounted and which is cooperable with lateral mold parts and a bottom stamp for molding a sole onto the shoe shaft, the last having a groove therein which contains a profile band of flexible material, the profile band being capable of contacting the inside surface of the shoe shaft opposite the sealing edges of the lateral mold parts during molding of a sole thereon.
According to known technology, shoe shafts to which soles can be molded may comprise an upper part and an insole, or they may be formed of only an upper part. The upper part may consist of leather, fabric, laminated fabric, elastomer or synthetic material such as polyvinylchloride or polyurethane, and it may have a vamp or appliques sewn or stitched thereto. In molding soles to the shoe shafts, shoe soling devices with several work stations, constructed as round table installations, are generally used.
The work stations utilize at least one last, two lateral mold parts and at least one bottom stamp. In a working position, i.e., in the position in which a sole is molded to the shoe shaft, the lateral mold parts are in a locked position in which they enclose an opening into which at least one injection channel opens. The last with mounted shoe shaft is arranged between these lateral mold parts in a locked position, whereby it encloses, together with the lateral mold parts and the bottom stamp, the molding cavity for the sole to be molded. The sole material is introduced through the injection channel(s) into this molding cavity.
In general, the soles molded onto the shoe shafts include a wear resistant outer sole and a flexible intermediate sole. It is also possible to mold only outer soles onto the shoe shafts.
The molds for the work stations are made from sample molds. For the production of a new shoe model, the shoe maker provides the mold maker with pairs of shoe shafts for various shoe sizes. The mold builder then produces the sample molds for each pair of matching shoe shafts, which then serve as models for the molds to be made for the work stations. The sample molds and working molds are made with great precision so that, among other things, during the molding of the soles to the shoe shafts, the sole material injected into the mold cavities is distributed in such a manner that perfect soles having no engraving errors, and particularly no air bubbles, are formed.
Particular problems result from the fact that during the molding of the soles, the shoe shafts mounted on the lasts are supposed to rest with sufficient pressure against the sealing lips of the lateral mold parts to prevent an extrusion of sole material from the mold cavity past the sealing lips onto the upper part of the shoe, whereas on the other hand the surface pressure of the sealing lips against the upper part of the shoe is not so high that permanent pressure marks are left on the upper part of the shoe. Until now, only trade-offs were possible to deal with these two contradictory requirements, i.e., no satisfactory solution existed.
According to current procedures the undesirable extrusion has been simply tolerated, and after the molding of the soles the undesirable extrusion has been manually removed and, simultaneously, the damaged parts, particularly the delicate upper parts of shoes made from soft leather, retouched with colored pencils or the like. However, this manual procedure is very expensive and has only been done because shoes with visible pressure marks from the sealing lips on the upper part of the shoe were not salable and generally had to be rejected as waste.
Problems also result from the fact that shoe shafts made from leather can have varying thicknesses, not only one from another, but in various areas of the same shoe shaft. This is of particular concern if these thickness variations, generally in the range of a few tenths of a millimeter, are in the area of the sealing lips of the lateral mold parts.
Shoe shafts generally have a toe vamp and/or a heel vamp and/or lateral vamp against which the sealing lips of the lateral mold parts rest during the molding on of the soles. The vamp generally is sewn on or stitched and forms an edge at its end in an area of the shoe shaft where it is particularly easy for sole material to be extruded during the molding of the soles.
In general workers have made do by gluing aluminum strips on the last in these areas in order to at least reduce the extrusion or, with thicker vamps, a portion of the last in the area of the vamp has been removed. However, this processing of lasts has the special disadvantage that it cannot be used if, during the further molding on of soles, shoe shafts with other vamps or even without vamps are used. The use of adhesive strips is also considered to be a stop-gap measure because the vamp can never be stitched or sewn so exactly onto the shoe shafts that it will always be in the same position, so that during the molding on of the soles in indetermined successions, there may be more or less extrusion at various places.
On the other hand, it is known to use lasts which include a profile band of elastic material. See, for example, German Patent Publication No. 21 63 455. These lasts are made of one piece and have a continuous, closed track groove into which the profile band of a flexible material is inserted, the groove being located in the last opposite the sealing lips of the cooperating lateral mold parts. The lateral mold parts also have grooves with inserted profile bands. It is hereby only possible to utilize the molding capability of the profile band.
During the molding on of a sole onto a shoe shaft, the upper part of the shoe is clamped between the two profile bands and the upper part of the shoe sealed against the sole material. Due to the fact that the profile bands fill the grooves in which they are positioned, a secure sealing or a prevention of lasting impressions is only possible for slight tolerance deviations in the shoe shafts and generally fail altogether for shoe shafts with vamps.
In addition, these known lasts with profile bands inserted into grooves are made in one piece. However, two-part lasts are generally used, particularly in shoe soling machines constructed as round table installations. They have a toe part and a heel part, connected by a joint. With this construction of the lasts it is possible to imitate the foot motion when slipping into the shoe for the mounting of the shoe shafts and to thus prevent inadmissibly high expansion of the upper material, which, in general, leads to permanent loss of shape. This can be applied correspondingly to the removal of the finished shoe from the lasts.